1. Field of the Invention
This invention relates to an electrical resistive material used to make, for example, a heating element for a thermal printing element.
2. Description of the Prior Art
There are known thin film resistive materials, such as a nickel-chromium alloy and a tantalum compound, which are used for thin film resistors. These materials, however, have a resistivity which is as low as about 0.2 m.OMEGA..multidot.cm, and it has, therefore, been difficult to make small resistors, such as chip resistors, having high resistance. The known chip resistors, for example, have only a maximum resistance of several tens to one hundred kilohms.
There are also known several kinds of thin film materials developed for making heating elements for thermal printing elements, and having a higher resistivity. These materials, however, have a very high temperature coefficient of resistance (TCR) in the order of several hundred ppm/.degree. C. which is too high for any precision resistor. For example, a known Ta--Si--C alloy has a temperature coefficient of resistance which is as high as about -600 ppm/.degree. C., though it has a relatively high resistivity of about 4.2 m.OMEGA..multidot.cm.
Yoshizaki, one of the inventors of this invention, et al. have developed an amorphous electrical resistive material composed of a Cr--Al--B ternary alloy and oxygen in order to overcome the drawbacks of the known materials as described above. This material is used for making thin film chip resistors and heating elements for thermal printing elements. It is produced by adding 10 to 30 at % (atomic %) of oxygen to a ternary alloy obtained by adding 30 to 70 at % of boron to a chromium-aluminium alloy containing 10 to 40 at % of aluminium, and is disclosed in the Japanese Patent Laying-Open Gazette No. 2-87501, laid open on Mar. 28, 1990. This material has, however, been found still unsatisfactory, since it undergoes crystallization and has a lower electric resistance when exposed to a high temperature. When it is used to make a heating element for a thermal printing element which will be exposed to a high temperature, it has been necessary to thermally treat it at a higher temperature to make a thermally stable heating element. The heat treatment has not only meant extra work, but also brought about a change in resistance of the material which is difficult to control.